With the growing trend toward unified communications, IPTV, collaborative applications in homes and enterprises, and the corresponding increasing demand for high throughput wireless communication, Multiple Input Multiple Output (MIMO) has become one of the key technologies for future wireless networks. MIMO combines multiple omni-directional antennas with signal processing techniques to extend the dimension of available radio resources to the time, frequency and space. Adopted in many standard protocols, e.g. IEEE 802.11n Part 11, it has been widely deployed to transport streamed voice and high-definition video traffic which requires high throughput.
Another wireless technology that has long been receiving interests is directional antennas, which use predetermined narrow beams to focus RF energy toward desired receivers. This achieves throughput gains and reduces interference. Moreover, the directivity of antennas facilitates determining proper orientation of the antenna, notably in outdoor environments allowing for a line-of-sight path. Recently, it has been shown that directional antennas in indoor environments provide a few strong paths between nodes even in absence of a line-of-sight path.
The combination of MIMO and directional antennas has been discussed by N. Razai-Ghods, M. Abdalla and S. Salous in “Characterization of MIMO propagation channels using directional antenna arrays,” Proc. IEEE Sarnoff Symp., Princeton, N.J., USA, March 2009. However, the results are based upon fixed orientation of the directional antennas, which led to the conclusion that the benefit of using directional antennas is marginal at best.
C. Hermozilla, R. Feick, R. A. Valenzuela and L. Ahumada, in “Improving MIMO capacity with directive antennas for outdoor-indoor scenario,” IEEE Trans. Wireless Comm., vol. 8, no. 8, pp. 2177-2188, May 2009, discuss using MIMO and directional antennas in a scattering-poor environment.
In a related field, using MIMO and directional antennas, “Demystifying beamforming”, (http://www.nowire.se/produktblad/Ruckus/Beamforming-WP-030909.pdf), by Ruckus Wireless, Inc., Sunnyvale, Calif., USA, discusses collecting packet error rates for determining the orientation of multiple antennas. A related rate adaptation algorithm is discussed by J. C. Bicket in “Bit-rate selection in wireless networks”, PhD dissertation, MIT, Boston, Mass., USA, 2005.
U.S. 2006/0234777 A1 discloses a radio access network having multiple sectors and comprising two or more sector transmitters serving respective sectors for transmitting data to mobile stations.
Muhammad Fainan Hanif, Peter J. Smith, Desmond P. Taylor and Philippe A. Martin, in “MIMO Cognitive Radios with Antenna Selection”, IEEE Trans. Wireless Comm., vol. 10, no. 11, pp. 3688-3699, November 2011, discuss using antenna selection to jointly satisfy interference constraints in multi-primary-user environments while improving achievable rates.
Jun Zhou, John Thompson and Ioannis Krikidis, in “Multiple Antennas Selection for Linear Precoding MISO Cognitive Radio”, Wireless Communications and Networking Conference, 5 Apr. 2009, discuss antenna selection algorithms for frequency reuse in cognitive radio settings.
Anand Prabhu Subramanian, Henrik Lundgren, Theodoros Salonidis and Don Towsley, in “Topology Control Protocol Using Sectorized Antennas in Dense 802.11 Wireless Networks”, present a measurement-based optimization framework for minimizing network interference and maximizing network capacity.